Straw Incorporation/Green Manuring 93

Straw Incorporation/ Green Manuring - 93
Project Leader and Principal UC Investigators G. Stuart Pettygrove, extension soils specialist, Department of Land, Air and Water Resources, UC Davis J.F. Williams, farm advisor, Sutter/Yuba Cooperative Extension S.C. Scardaci, farm advisor, Colusa County Cooperative Extension R.K. Webster, Department of Plant Pathology, UC Davis J.E. Hill, Department of Agronomy and Range Science, UC Davis	This five-year-old project is exploring many facets of the relationships between incorporating rice straw and its resulting impact on rice plant nutrition, disease incidence, grain yield and related factors. Additionally, researchers are working on two other related objectives: Development of soil and plant nitrogen diagnostic methods that will assist growers in N fertilizer rate decisions in unburned rice production. Demonstrate the cumulative effect of winter green manure production (compared to winter fallow) on rice grain yield, nitrogen requirement, and stem rot severity under different straw management practices. Previous work concentrated on a 15-acre portion of a farm in southern Sutter County. Researchers continue to analyze data from a continuous rotation of rice and purple vetch under three different residue management strategies - fall burned, fall incorporated and spring incorporated. Each treatment is replicated on one-acre plots. In 1993, however, scientists expanded their examination of different incorporation methods to three additional farm with similar soil characteristics, straw management scenarios and other management factors. The other sites included farms in Colusa County, Butte County and Sutter County. The following summarizes the significant findings. Diagnostic Tools In their research into diagnostic methods to assist growers in determining fertilizer nee&, researchers found that measurements of soil organic carbon, total nitrogen and incubation ammonium content did not serve as good predictors of rice grain yields. However, use of a chlorophyll meter at panicle initiation did prove very useful in judging nitrogen status, as it has done consistently for three years. The chlorophyll meter has the advantage of providing growers with an immediate diagnosis, one that has proven nearly as accurate as more time consuming laboratory analysis. Straw Incorporation Researchers found no consistent differences in grain yield between burned fields and straw-incorporated fields. However, at the long-term experiment the fall-incorporated plots are averaging 4 hundredweight/acre higher maximum yield than fall-burned plots. Spring incorporated plots resulted in 1.8 hundredweight/acre higher yield. Researchers aren't exactly sure why. Neither loss of nitrogen by burning nor disease differences appear to account for the yield difference. Another important observation was that straw- incorporated plots required more nitrogen to achieve maximum yield than burned plots. Contrary to what you might expect, stem rot ratings were not higher on incorporated plots than they were on fall-burned plots. However, researchers found an increased level of aggregate sheath spot in the range of 10-20 percent on spring-incorporated plots than on either the fall-burned plots or the fall-incorporated plots. Yields on unfertilized plots have declined over four years; aggregate sheath spot may be responsible. Green Manuring Up through 1992 a "green manure" crop of purple vetch at the Sills Farm provided a nitrogen fertilizer replacement value of 60 to 108 pounds N/acre. During the winter of 1992-93, however, heavy rains and saturated soil conditions significantly diminished purple vetch yield, with a resulting, very low nitrogen contribution of only 6 to 13 pounds N/acre. After five years in this study, the promising role green manuring can play in rice cultivation has become increasingly apparent. Unfertilized plots in a rice-winter purple vetch rotation are yielding up to 15 to 27 hundredweight grain more than continuous winter fallow plots. More importantly, under all three straw management systems at the Sills Farm in three out of four years, green manured plots exceeded yields on winter fallow plots. The four-year average annual yield benefit of green manuring ranges from 0.7 to 3.1 hundredweight/acre. Green manuring effects on severity and incidence of stem rot and aggregate sheath spot, while not significant, appear to be entirely a result of the increased nitrogen supply to rice.

Straw Incorporation/
Green Manuring - 93

Project Leader and Principal UC Investigators

G. Stuart Pettygrove, extension soils specialist, Department of Land, Air and Water Resources, UC Davis

J.F. Williams, farm advisor, Sutter/Yuba Cooperative Extension

S.C. Scardaci, farm advisor, Colusa County Cooperative Extension

R.K. Webster, Department of Plant Pathology, UC Davis

J.E. Hill, Department of Agronomy and Range Science, UC Davis

This five-year-old project is exploring many facets of the relationships between incorporating rice straw and its resulting impact on rice plant nutrition, disease incidence, grain yield and related factors. Additionally, researchers are working on two other related objectives:

Development of soil and plant nitrogen diagnostic methods that will assist growers in N fertilizer rate decisions in unburned rice production.
Demonstrate the cumulative effect of winter green manure production (compared to winter fallow) on rice grain yield, nitrogen requirement, and stem rot severity under different straw management practices.

Previous work concentrated on a 15-acre portion of a farm in southern Sutter County. Researchers continue to analyze data from a continuous rotation of rice and purple vetch under three different residue management strategies - fall burned, fall incorporated and spring incorporated. Each treatment is replicated on one-acre plots. In 1993, however, scientists expanded their examination of different incorporation methods to three additional farm with similar soil characteristics, straw management scenarios and other management factors. The other sites included farms in Colusa County, Butte County and Sutter County. The following summarizes the significant findings.

Diagnostic Tools

In their research into diagnostic methods to assist growers in determining fertilizer nee&, researchers found that measurements of soil organic carbon, total nitrogen and incubation ammonium content did not serve as good predictors of rice grain yields. However, use of a chlorophyll meter at panicle initiation did prove very useful in judging nitrogen status, as it has done consistently for three years. The chlorophyll meter has the advantage of providing growers with an immediate diagnosis, one that has proven nearly as accurate as more time consuming laboratory analysis.

Straw Incorporation

Researchers found no consistent differences in grain yield between burned fields and straw-incorporated fields. However, at the long-term experiment the fall-incorporated plots are averaging 4 hundredweight/acre higher maximum yield than fall-burned plots. Spring incorporated plots resulted in 1.8 hundredweight/acre higher yield. Researchers aren't exactly sure why. Neither loss of nitrogen by burning nor disease differences appear to account for the yield difference. Another important observation was that straw- incorporated plots required more nitrogen to achieve maximum yield than burned plots.

Contrary to what you might expect, stem rot ratings were not higher on incorporated plots than they were on fall-burned plots. However, researchers found an increased level of aggregate sheath spot in the range of 10-20 percent on spring-incorporated plots than on either the fall-burned plots or the fall-incorporated plots. Yields on unfertilized plots have declined over four years; aggregate sheath spot may be responsible.

Green Manuring

Up through 1992 a "green manure" crop of purple vetch at the Sills Farm provided a nitrogen fertilizer replacement value of 60 to 108 pounds N/acre. During the winter of 1992-93, however, heavy rains and saturated soil conditions significantly diminished purple vetch yield, with a resulting, very low nitrogen contribution of only 6 to 13 pounds N/acre.

After five years in this study, the promising role green manuring can play in rice cultivation has become increasingly apparent. Unfertilized plots in a rice-winter purple vetch rotation are yielding up to 15 to 27 hundredweight grain more than continuous winter fallow plots. More importantly, under all three straw management systems at the Sills Farm in three out of four years, green manured plots exceeded yields on winter fallow plots. The four-year average annual yield benefit of green manuring ranges from 0.7 to 3.1 hundredweight/acre.

Green manuring effects on severity and incidence of stem rot and aggregate sheath spot, while not significant, appear to be entirely a result of the increased nitrogen supply to rice.